Recently, due to the rapid rise in international oil prices and the introduction of greenhouse gas reduction goals for solving the global warming problem, research into new & renewable energy capable of replacing fossil fuels has attracted attention throughout the world. In particular, Korea, which is dependent on imports for more than 97% of its energy, has set a goal of supplying 5% of its total energy using new & renewable energy sources in order to fundamentally improve the structure of the energy industry. With regard to photovoltaic generation systems, a project to build one hundred thousand solar homes, a general popularization project and a local popularization project are rapidly being conducted under the guidance of national and local governments.
In particular, a grid-interactive photovoltaic generation system attracts attention. In general, a grid-interactive photovoltaic generation system refers to a photovoltaic generation system that interacts with a grid power source. In detail, a grid-interactive photovoltaic generation system is a system that receives power from a grid power source when power produced through photovoltaic generation is smaller than power consumed by a load, and supplies surplus power to the grid power source when power produced through photovoltaic generation exceeds power consumed by a load, thereby improving overall operational efficiency.
*4In general, a grid-interactive photovoltaic generation system includes solar cells, an MPPT converter, and an inverter for supplying power, produced by the solar cells, to a grid.
Such a conventional grid-interactive photovoltaic generation system has a problem in that the rate of utilization thereof is very low compared to the high installation costs thereof because it can be used only in the daytime, during which solar radiation exists, due to the use of a method of simply supplying power, generated using solar light, to a grid under the MPPT control of a converter (inverter). Furthermore, there is another problem in that the power factor of a grid is degraded due to the supply of active power through photovoltaic generation when the conventional grid-interactive photovoltaic generation system is applied to a nonlinear and power factor load, such as a house or an office building. Furthermore, the conventional grid-interactive photovoltaic generation system has a problem in that the extent of utilization, such as operation in conjunction with other systems, is low, compared to the high installation costs thereof.